RO116567B1 - Process for producing cellulose moulding bodies - Google Patents

Abstract

The invention relates to a process for producing moulding bodies from cellulose dissolved in an aqueous solution of tertiary amine-oxide, wherein, during the transporting step, the cellulose solution is transported through the components of an installation at different flow rates. A hole is made in a spot of a component of the installation where the flow rate is relatively low in comparison with the rate of the main solution stream, in order to prevent the formation of cellulose solution standstill areas in the installation applying the process and the degradation of the cellulose solution, said hole being meant to discharge a fraction of the cellulose solution.

Description

The invention relates to a process for obtaining formation bodies, from cellulose dissolved in an aqueous tertiary amino acid solution, in which, in the transport phase, the cellulose solution is conveyed at different flow rates through the component parts of the installation.

For the purposes of this specification, the term "viscous mass" or "spinning mass" refers to a solution containing cellulose and a diluted tertiary amino acid which serves to manufacture a wide range of cellulose products - in particular in the form of fibers and foils. For the sake of simplification, for the preparation and further processing of the spinning mass, the generic name of the process has been adopted.

Tertiary amino acids are known as potential cellulose solvents. Thus, for example, from US Patent Documentation 217918 * 1, it is known that tertiary amino acids can dissolve cellulose without the formation of derivative compounds and that, from these solutions, various cellulose-based products can be obtained by precipitation. for example, L5 cellulose fibers. Other types of tertiary amino acids are subject to patent documentation EP-A0553070. For the sake of simplification, the following has been adopted the generic name NMMO (N-methylmorpholine-N-oxide) which refers globally to all tertiary amino acids having the ability to dissolve cellulose.

From the point of view of an alternative solvent, tertiary amines-oxides have the advantage that, unlike what happens in the viscous process, cellulose is not dissolved by NMMO with the formation of derivative compounds and therefore does not have to be chemically regenerated, NMMO remains chemically unchanged, passes to precipitate in the spinning bath and can be recovered and reused when preparing a new solution. The NMMO process thus offers the possibility of achieving a closed circuit of the solvent. In addition, NMMO exhibits a reduced degree of toxicity.

However, it should be taken into account that, by dissolving cellulose in NMMO, its degree of polymerization is diminished. In addition to this, and especially in the presence of metal ions (eg Fe ³⁺ ), it is possible to initiate chain cleavage processes of the radicals and thus to a marked degradation of both cellulose and 30 and the solvent (see: Buijtenhuijs et al .: The Degradation and Stabilization of Cellulose Dissolved in N-Methylmorpholin-N-Oxide (NMMO) published in Das Paper ⁴ ', Year 40, No.12, pp. 615-619, 1986).

In general, it can be stated that the amino acids also have a limited thermal stability and depend on their structure. The NMMO monohydrate is under normal conditions in the form of a white crystalline compound, which melts at 72 ° C. However, the anhydrous compound melts only at a temperature of 172 ° C. By heating the monohydrate, there is a marked change in color beyond the temperature of 12O / 13O ° C, above 175 ° C an exothermic reaction is triggered, accompanied by a complete dehydration of the melt, with energetic release of gas 40 and explosive behavior, reaching thus at temperatures exceeding 25 ° C.

It is known that the presence of iron or metallic copper and, in particular, of their salts, leads to a sensitive drop in NMMO decomposition temperatures, together with an increase in decomposition rates.

In addition to the above, the following problem also occurs: the thermal instability of NMMO and cellulose solutions.

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It is about the fact that in the solutions subjected to high processing temperatures (about 11O ... 12O ° C) some uncontrollable processes of dissociation can be triggered, which can lead, by gas release, to strong detonations, fires and even explosions. .

The preparation and processing, on a large scale, of cellulose solutions in a dilute amino acid are carried out in industrial installations whose components are mainly made of iron and steel, and which also include a variety of auxiliary equipment, for example: pipes, filters, pumps, taps or buffers - all made of iron or steel. Basically, all the component elements are characterized by the fact that in them there are a series of processes that influence the parameters of the cellulose solution flow 55 and which, in the case of high viscosity solutions, usually lead to different speeds of flow of the solutions at the moment of the process. various components.

Certain components that come into the composition of a cellulose-based product manufacturing facility that work according to the amino acid process are characterized by the fact that they have areas where the flow rates of a cellulose solution 6 decrease and approach zero. Such areas of stagnation of the flow are called dead zones.

Bypassing and avoiding these dead zones where the environment is exposed for a long time to thermal demands and becomes degraded, in the sense of the above, and in which a repeated process of corrosion of the metal from which the components are made and takes place the devices that come into the composition of an installation are one of the major objectives of improving the process configuration after which the amino acid process is carried out, in order to increase its reliability.

Particularly dangerous are those dead areas, which allow 70 degraded solutions to be recirculated, in the main flow of viscous and thermally unstable cellulose solution, to which the content in metal parts has increased, possibly as a result of material corrosion processes. of which the various component elements are executed at the mechanical actuation of the respective components.

Due to the tight fit between the moving parts (so-called metal sealing) that is found in the usual commercial equipment and machinery, as well as the high viscosity of the solution, the flow rates of the affluent solution vary depending on the accuracy of the adjustment. local and to be located, as a whole, at extremely low levels. under these conditions, the solution is exposed for three days or even weeks to the temperature regime of the respective part and therefore subject to the degradation process described above; It should be mentioned that due to the small mass of solution that has penetrated this space, the heat of reaction developed by the exothermic processes is completely discharged. Solution degradation processes can progress to such an extent that, over time, metal-containing deposits will no longer have flow characteristics; the iron content of these deposits may even represent a few percent by weight, regardless of whether or not higher-grade steel parts would have been used.

In the conditions in which such residues and deposits have formed, the displacement of the piston during the operations of washing the filter in reverse circuit or changing the sieve can lead to the introduction in the system of these residues, which can trigger, for example, a series of exothermic processes in the production flow. 90

In the patent documentation EP-A-0652098 there is presented a process for filtering a thermally unstable melt of polymers, which aims to avoid the appearance of dead zones. The objective thus defined is achieved, according to the process envisaged, in that the polymer melt is introduced from the bottom up, by pumping, into the pipe beam of a heat exchanger, the respective pipes being immersed in the mass of the thermal agent in liquid state; In each of the pipes of the heat exchanger, a filter-candle is mounted such that it is fitted so as to obtain an outer annular slot; the main flow of polymer melt, which passes through the candle filters, and a secondary flow, which does not pass through the candle filters, is discharged to the top of the heat exchanger tubing and mixed.

The technical measures to prevent the formation of dead zones are presented, for example, in the publication WO 94/02408 and they are based on a sealing principle which aims to prevent the penetration of the spinning mass between the mobile components of the tank.

Given that the process described above, for sealing dead areas, either cannot be applied in various situations in which moving parts occur, or cannot provide adequate and lasting reliability, the present invention aims to , in the transport phase of a cellulose solution dissolved in an aqueous tertiary amino acid solution, to achieve a sufficiently high rate of flow of the cellulose solution when crossing the various component parts, so as to eliminate the disadvantages exhibited more and ensure that the respective cellulose solution is safely transported.

The process which is the subject of this invention solves the problem proposed by the fact that, at a point in a component part of the installation, in which the flow velocity is relatively low compared to the speed of the main solution current, an orifice through which an evacuation is practiced fraction of cellulose solution.

The expression is removed from a component part refers to the fact that part of the cellulose solution is taken from the main stream and that this fraction does not return to the main stream.

The relatively low expression refers to the fact that the flow rate of the cellulose solution is related to that of the main current, which runs through the respective part. The basis of the invention is the finding that the problems created by the solution degenerated by cellulose, which adhere to the metal surfaces near the dead zones, cannot be solved effectively by sealing the parts as completely as possible in order to avoid the formation of dead zones, so as tried by applying the solutions belonging to the prior art, but on the contrary, by providing an orifice near the dead zones, through which the cellulose solution can be evacuated, thus avoiding its accumulation and decomposition.

The orifice through which the cellulose solution is discharged may be, for example, a hole, slot or similar, which may suitably allow the cellulose solution to be evacuated under the conditions dictated by the mode of operation.

According to the provisions of the invention, the creation of such an orifice avoids the accumulation and decomposition of the filtration mass in the dead zones.

In a preferred embodiment of the process which is the subject of the present invention, it is provided that the orifice practiced in the component part of the installation is so formed as to allow the removal of the cellulose solution having a temperature.

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140 'of growth which is up to 10 ° C, preferably up to 5 ° C, below the growth temperature of the cellulose solution being transported.

It was found that the thermal stability of a cellulose solution decreases as the time required for its evacuation through the respective hole increases. The preferred embodiment of this process, mentioned above, is an indication for a specialist that the outlet of the cellulose solution must be properly formed.

For the purpose of the process of this invention, the component part in which an orifice is provided may be, for example, a filter, pump, flange, valve or recirculating washer.

The advantages of the invention consist in the fact that a completely new way of organizing the process within the amino acid process has been developed and that consists in avoiding the formation of dead zones and by providing holes in each component part. evacuation of the viscous solution of cellulose that accumulates in the respective components. The orifice must be so designed and constructed that the rate of discharge of the product is sufficiently high for the degradation process to which the spinning mass is subjected, which is dependent on temperature and stagnation duration, to develop to such an extent that , by mixing a determined quantity of mass discharged from the respective component with a certain amount of intact spinning mass, the thermal stability of the downstream spinning mass is not significantly affected.

It could be established that an acceptable solution is reached, both economically and in terms of process reliability, when it is ascertained based on the results provided by the experienced verification - that by an addition of evacuated mass, representing 1% (relative to the intact spinning mass), a spinning mass is obtained whose thermal stability is less than 10 ° C lower than the thermal stability of the same intact spinning mass, but without addition.

The term "intact spinning mass" refers to the spinning mass belonging to the main flow carried by the respective component.

In the following, examples are presented that serve to detail the invention in connection with FIG. 1 ... 4, which represents:

FIG. 1, the graphical representation of the temperature variation on the parts of the installation and the temperature differences between the temperature of a sample and that of the different parts of the installation - control curves;

-fig.2a and b, schematic representation of a section through a buffer device with storage space at an installation for carrying out the process according to the invention;

- Fig. 3, schematic representation of the section through a spherical valve, at an installation for carrying out the process according to the invention;

- Figs. 4a and 4b, schematic representation of the section through a washing filter with reverse circuit, at an installation for carrying out the process according to the invention.

Example 1. Thermal stability test

1. Intact spinning table (control)

The intact spinning mass (composition: 15% cellulose, 75% NMMO, 10% H ₂ 0), in a solid, crystallized state, was finely ground in a laboratory mill.

The test was performed in a Sikarex oven (type: TSC 512 manufacturer: Systag), for which purpose a quantity of 11.5 g was taken from the sample prepared as it was

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RO 116567 Bl shown above, which was inserted into a closed pressure vessel and lined with glass, and then subjected to heating. The adopted heating program was one of the step heating programs, developed by Standard Software, which provides that between two isothermal stages (step I - 9O ° C, step 2 - 18D ° C) the heating should be extremely slow (with a temperature increase gradient of 6 ° C / h). It was thus possible to establish that in the reference area a process with a dynamic deployment was installed, which ensures a very high reproducibility of the exothermic processes. During the heating process, the temperature difference between the temperature of the heating jacket (TM) and the sample temperature (TR) was determined continuously. The data collected were processed using a computer.

A representative result of these determinations appears in Fig. 1 in the form of a curve A (control), where in the abscissa the values of the heating mantle temperature (above 10O ° C) are passed and in order the temperature differences (in ° C) between the temperature of the sample and that of the heating jacket (TR-TM). Curve A shows that, for mantle temperatures up to 15 ° C, no exothermic reaction occurs in the mass of the sample, since during the entire heating period the sample temperature is constant about 5 ° C lower than mantalei temperature. This corresponds to a normal heating process and which takes place under the conditions of the temperature gradient mentioned above.

Since the mantle temperature has reached a value of about 15 ° C, the A curve has a more pronounced ascending edge, which shows that the sample temperature rises faster than the mantle temperature. This is due to exothermic reactions taking place in the mass of the sample. At a mantle temperature of about 165 ° C the temperature difference is about 1 ° C, which allows us to conclude that the sample temperature is about 175 ° C.

2. The residue taken from a filter plunger in the next step was repeated the test, using 11.5 g taken from the finely ground spinning mass, mentioned above and intimately mixed with □, 115 g (= 1%) by mass. subject to verification and which came from the deposits formed on the piston of a filter with reverse circuit wash, belonging to the known state of the art according to fig.4b. The test results are shown in Fig. 1 in the form of a curve B.

The curve shows that exothermic reactions occur in the mass under test starting with a temperature of about 12 ° C, which proves that the mixture has a lower thermal stability than that of the intact spinning mass (see control curve A).

3. Exfiltrated mass according to the invention finally proceeded to repeat the test described above in point 2, using this time exfiltrated mass, discharged through the slot created between the piston and the wall, to a filter according to fig.4b. The results of the determination are shown in Fig. 1 in the form of a curve denoted by C.

From examining this curve it can be concluded that the mass subjected to the test is characterized by a significantly higher thermal stability, compared with that of the deposits formed in an installation belonging to the known state of the art. It can also be seen that the thermal stability of the mass under test differs insignificantly from that of an intact spinning mass (see control curve A).

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4. Check the efficiency of an exfiltration hole

In order to verify that the office practiced according to the provisions of this invention, in a certain component element, is capable of ensuring the sufficiently rapid evacuation of the spinning mass, the thermal stability of the intact spinning mass is determined (see paragraph 1 above), after which proceeds to determine the same parameter for a mixture consisting of intact spinning mass and an addition of 1% by weight (relative to intact spinning mass) taken from the exfiltrated mass (see paragraph 3 above). It is considered that the orifice guarantees, within the meaning of the present invention, a sufficient degree of safety in the process, if the thermal stability of the mixture differs only slightly with the thermal stability of the intact spinning mass. For the purposes of the present description and the present claims, the so-called rising temperature is defined. Rising temperature means that temperature of the jacket (programmed temperature) at which the temperature of the sample sample is, due to exothermic reactions, 1O ° C above the temperature of the heating jacket.

For the purposes of the present description and the present claims, it is considered that the thermal stability of the mixture differs only slightly from the stability of the intact spinning mass when the growth temperature of the mixture and that of the intact spinning mass differ by at most 10 ° C.

For a better understanding, this determination principle is exemplified on the basis of the data provided by fig. 1.

According to the methodology presented above, we start by drawing the curve A for an intact spinning mass. This curve A shows that the intact spinning table has a growth temperature of about 165 ° C.

Then proceed to the preparation and testing of the mixture consisting of intact spinning mass and exfiltrated mass. Admitting that the curve C of FIG. 1, it is found that the growth temperature of a homogeneous mixture is around 163 ° C. This means that the difference between the two values of the rising temperature (165-163 ° C) is 2 ° C and that, in the sense of the present invention, the hole through which the exfiltrated mass has been evacuated is properly formed, because between the stability the thermal difference of the mixture and that of the intact spinning mass is a minor difference.

Figure 2 to 4 below shows schematically the methods of practicing, according to the provisions of the present invention, holes in various component elements, so as to ensure the evacuation of a cellulose solution.

Figs. 2a and 2b show schematically sections through a buffer device with a storage space 1, for receiving the spinning mass, and at which the dimensions of storage space 1 can be adjusted by displacing a cylindrical piston 2a and 2b respectively. Storage space 1 is fed with spinning table through channel 3a and 3b respectively. The reference symbols 4a and 4b respectively refer to the evacuation channels. The reference symbols 5a and 5b respectively refer to the housing of the buffer container. Such a buffer device is used in reverse circuit wash filters and is called the reverse circuit wash injector.

Fig. 2a shows a buffer device in the solution corresponding to the known state of the art, in which the piston 2a is pressed tightly, ie practically without a gap

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EN 116567 Exfiltration block, in the cylindrical storage space * 1. However, practice has shown that, however, there is a dead zone between the outer surface of the piston and the wall of the cylindrical storage space. Due to the displacement of the piston 2a, on its surface deposits of spinning mass are formed subjected to a decomposition process depending on the temperature and the stagnation time, which can lead to the extraction of metal ions from the outer surface of the piston.

According to the provisions of this invention, such situations can be avoided by providing a slot between the piston 2b (see fig.2b) and the cylindrical wall of the storage space 1; its dimensions can be such that - depending on the pressure regime inside the storage space and the viscosity of the spinning mass - in any of the working positions of the plunger ensure that a sufficient amount of spinning mass is evacuated and thus the formation is avoided. of dead zones, as well as the formation of deposits on the piston surface. In this way, the condition stated above is satisfied, in terms of ensuring sufficiently high thermal stability. The spinning mass that is evacuated is marked in fig.2b by two arrows directed obliquely upwards.

Example 2. In Figure 3, a section through a spherical valve is shown schematically. Reference symbol 5 refers to a lever with which the valve can be opened or closed. With 6a and 6b the glands are identified which, in turn, can be adjusted by means of the sliding parts 7a and 7b respectively. The reference symbol 8 serves to identify the outlet orifice designed according to the provisions of the present invention and by which an amount of spinning mass from space 9 of the spherical valve can be eliminated. The spinning mass that comes out of the ball valve is identified by an arrow pointing down. And in this case the principle that the dimensions of the orifice are considered to be correctly chosen applies, when the expelled spinning mass fulfills the conditions set out in the thermal stability criterion above.

Example 3. Figure 4 shows schematically sections through a filter with washing in reverse circuit. With the reference symbols 1Oa and 10b respectively, the intake channels of the spinning mass subjected to filtration are noted, the symbols 11a and 11b respectively refer to the discharge channels, with 12a and 12b respectively the pistons provided with the filters 13a and 13b respectively, and the symbols 14a and 14b respectively serve to identify impurities evacuation channels. With 15a and 15b respectively the casing components are noted, and the symbols 19a and 1Bb respectively refer to the holes for impurities.

in the case of pistons 12a and 12b, they find, in principle, the indications of composition previously stated in relation to pistons 2a and 2b of fig.2a respectively 2b; realizing a slot between the cylindrical wall of the piston 12b and the inner wall of the housing 15b, according to the provisions of the present invention, is the appropriate solution that allows the removal of a quantity of spinning mass and eliminates the danger of forming deposits, as they occur in a washing filter. in the reverse circuit according to FIG. 4a.

It was thus found, for example, that in the extremely small space formed between the piston and the casing at a spinning aggregate with an inverse washing circuit (Fig. 4a) it can penetrate an extremely small amount of cellulose solution, then subjected total degeneration.

Claims (4)

1. Process for obtaining cellulose forming bodies dissolved in an aqueous tertiary amino acid solution, in which, in the transport phase, the cellulose solution is conveyed at different flow rates through the component parts of an installation, characterized in that that, at a point in a component part of the installation, where the flow rate is relatively low compared to the speed of the main solution current, an orifice is made through which a fraction of the cellulose solution is evacuated. 2. Process according to claim 1, characterized in that the hole in the component part of the installation is so designed and constructed as to allow the cellulose solution having a growth temperature which is at most 1O ° C below the growth temperature to be evacuated. of the cellulose solution being transported. 3. Process according to claim 1, characterized in that the hole in the component part of the installation is so designed and constructed as to allow the cellulose solution having a growth temperature which is at most 5 ° C below the growth temperature to be evacuated. of the cellulose solution being transported. 4. Process according to claim 1, characterized in that the component part of the installation, in which an orifice through which a fraction of cellulose solution is discharged, is a filter, pump, valve, flange or washer injector. with recirculation.